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Dec. 5, 2011 -- Newer antidepressants are all about equally effective, according to a new analysis, but that doesn't mean they work the same way for everyone.

"Contrary to drug industry claims, scientific evidence does not support the choice of one drug over another based solely on better effectiveness," says researcher Gerald Gartlehner, MD, MPH, a clinical epidemiologist at Danube University in Austria.

The study is published in the Annals of Internal Medicine. It was funded by the Agency for Healthcare Research and Quality.

Tracking the Newer Antidepressants

Most newer antidepressants prescribed to treat major depressive disorder are the so-called second-generation drugs. They work by affecting levels of brain chemicals such as serotonin or norepinephrine.

More than 16% of adults will be affected with major depressive disorder at some point, the researchers write.

Experts have debated which of the newer antidepressants are most effective. "Many individual studies have compared antidepressants for the treatment of depression," Gartlehner tells WebMD. "The results of the individual studies are mixed and sometimes contradictory, which can make it difficult for consumers to understand and interpret the results."

The researchers found 234 previously published, scientifically sound studies on antidepressants. They re-evaluated the results.

They looked at studies that compared two drugs to each other or a drug to a placebo. The majority of the studies, 77%, were funded by pharmaceutical companies. Some of the researchers also report consultant work for Novartis and for Takeda Pharmaceutical Company. Among the findings:

Overall effectiveness did not differ much among the drugs.

37% of people with acute depression who took the drugs did not improve by six or 12 weeks.

Newer Antidepressants: Differences

There weren't enough data to draw conclusions about differences among the medications concerning some side effects, such as suicidal thoughts. The researchers say suicide is ''relatively rare" and affects one in 8,000 patients treated with the drugs. They agree with an FDA analysis that finds the risk increases in children and young adults but not in people older than age 24 who take the drugs.

In seven studies, Wellbutrin was linked with less sexual dysfunction than Lexapro (escitalopram), Paxil (paroxetine), Prozac, or Zoloft.